Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $152.50   11.139%   $169.487   $169.49   $169.50   $169.50  
  Purchase #2 $95.39   11.255%   $106.1261   $106.13   $106.15   $106.10  
  Purchase #3 $73.40   8.474%   $79.6199   $79.62   $79.60   $79.60  
  Purchase #4 $168.78   9.492%   $184.8006   $184.80   $184.80   $184.80  
  Purchase #5 $222.82   13.453%   $252.796   $252.80   $252.80   $252.80  
  Purchase #6 $117.79   10.464%   $130.1155   $130.12   $130.10   $130.10  
  Purchase #7 $26.25   9.797%   $28.8217   $28.82   $28.80   $28.80  
  7 purchase totals = $856.93       $951.7668   $951.78   $951.75   $951.70